Implement simple cart system with FastAPI and SQLite

- Set up project structure with FastAPI and SQLite
- Create models for products and cart items
- Implement schemas for API request/response validation
- Add database migrations with Alembic
- Create service layer for business logic
- Implement API endpoints for cart operations
- Add health endpoint for monitoring
- Update documentation
- Fix linting issues

README.md

@@ -1,3 +1,111 @@
-# FastAPI Application
+# Simple Cart System
 
-This is a FastAPI application bootstrapped by BackendIM, the AI-powered backend generation platform.
+A simple shopping cart system API built with FastAPI and SQLite.
+
+## Features
+
+- Product management (CRUD operations)
+- Shopping cart functionality
+- User-specific carts
+- Stock management
+
+## Getting Started
+
+### Prerequisites
+
+- Python 3.8 or higher
+- pip (Python package manager)
+
+### Installation
+
+1. Clone the repository:
+
+```bash
+git clone <repository-url>
+cd simplecartsystem
+```
+
+2. Install the dependencies:
+
+```bash
+pip install -r requirements.txt
+```
+
+3. Run database migrations:
+
+```bash
+alembic upgrade head
+```
+
+4. Start the application:
+
+```bash
+uvicorn main:app --reload
+```
+
+The API will be available at http://localhost:8000.
+
+## API Documentation
+
+Interactive API documentation is available at:
+- Swagger UI: http://localhost:8000/docs
+- ReDoc: http://localhost:8000/redoc
+
+## API Endpoints
+
+### Health Check
+
+- `GET /api/v1/health` - Check API and database health
+
+### Products
+
+- `GET /api/v1/products` - List all products (with pagination)
+- `GET /api/v1/products/{product_id}` - Get a specific product
+- `POST /api/v1/products` - Create a new product
+- `PUT /api/v1/products/{product_id}` - Update a product
+- `DELETE /api/v1/products/{product_id}` - Delete a product
+
+### Cart
+
+- `GET /api/v1/cart` - View current cart
+- `POST /api/v1/cart/items` - Add item to cart
+- `PUT /api/v1/cart/items/{item_id}` - Update cart item quantity
+- `DELETE /api/v1/cart/items/{item_id}` - Remove item from cart
+- `DELETE /api/v1/cart` - Clear cart
+
+## Cart Usage Example
+
+### Add Product to Cart
+
+```bash
+curl -X POST "http://localhost:8000/api/v1/cart/items" \
+  -H "Content-Type: application/json" \
+  -H "user-id: user123" \
+  -d '{
+    "product_id": 1,
+    "quantity": 2
+  }'
+```
+
+### View Cart
+
+```bash
+curl -X GET "http://localhost:8000/api/v1/cart" \
+  -H "user-id: user123"
+```
+
+## Database Schema
+
+The system uses SQLite with the following main tables:
+
+- `products`: Stores product information
+- `carts`: Stores user cart information
+- `cart_items`: Stores items in user carts
+
+## Technology Stack
+
+- [FastAPI](https://fastapi.tiangolo.com/) - Web framework
+- [SQLAlchemy](https://www.sqlalchemy.org/) - ORM
+- [Alembic](https://alembic.sqlalchemy.org/) - Database migrations
+- [Pydantic](https://pydantic-docs.helpmanual.io/) - Data validation
+- [SQLite](https://www.sqlite.org/) - Database

alembic.ini

@@ -0,0 +1,110 @@
+# A generic, single database configuration.
+
+[alembic]
+# path to migration scripts
+script_location = alembic
+
+# template used to generate migration file names; The default value is %%(rev)s_%%(slug)s
+# Uncomment the line below if you want the files to be prepended with date and time
+# see https://alembic.sqlalchemy.org/en/latest/tutorial.html#editing-the-ini-file
+# for all available tokens
+# file_template = %%(year)d_%%(month).2d_%%(day).2d_%%(hour).2d%%(minute).2d-%%(rev)s_%%(slug)s
+
+# sys.path path, will be prepended to sys.path if present.
+# defaults to the current working directory.
+prepend_sys_path = .
+
+# timezone to use when rendering the date within the migration file
+# as well as the filename.
+# If specified, requires the python-dateutil library that can be
+# installed by adding `alembic[tz]` to the pip requirements
+# string value is passed to dateutil.tz.gettz()
+# leave blank for localtime
+# timezone =
+
+# max length of characters to apply to the
+# "slug" field
+# truncate_slug_length = 40
+
+# set to 'true' to run the environment during
+# the 'revision' command, regardless of autogenerate
+# revision_environment = false
+
+# set to 'true' to allow .pyc and .pyo files without
+# a source .py file to be detected as revisions in the
+# versions/ directory
+# sourceless = false
+
+# version location specification; This defaults
+# to alembic/versions.  When using multiple version
+# directories, initial revisions must be specified with --version-path.
+# The path separator used here should be the separator specified by "version_path_separator" below.
+# version_locations = %(here)s/bar:%(here)s/bat:alembic/versions
+
+# version path separator; As mentioned above, this is the character used to split
+# version_locations. The default within new alembic.ini files is "os", which uses os.pathsep.
+# If this key is omitted entirely, it falls back to the legacy behavior of splitting on spaces and/or commas.
+# Valid values for version_path_separator are:
+#
+# version_path_separator = :
+# version_path_separator = ;
+# version_path_separator = space
+version_path_separator = os  # Use os.pathsep. Default configuration used for new projects.
+
+# set to 'true' to search source files recursively
+# in each "version_locations" directory
+# new in Alembic version 1.10
+# recursive_version_locations = false
+
+# the output encoding used when revision files
+# are written from script.py.mako
+# output_encoding = utf-8
+
+sqlalchemy.url = sqlite:////app/storage/db/db.sqlite
+
+
+[post_write_hooks]
+# post_write_hooks defines scripts or Python functions that are run
+# on newly generated revision scripts.  See the documentation for further
+# detail and examples
+
+# format using "black" - use the console_scripts runner, against the "black" entrypoint
+# hooks = black
+# black.type = console_scripts
+# black.entrypoint = black
+# black.options = -l 79 REVISION_SCRIPT_FILENAME
+
+# Logging configuration
+[loggers]
+keys = root,sqlalchemy,alembic
+
+[handlers]
+keys = console
+
+[formatters]
+keys = generic
+
+[logger_root]
+level = WARN
+handlers = console
+qualname =
+
+[logger_sqlalchemy]
+level = WARN
+handlers =
+qualname = sqlalchemy.engine
+
+[logger_alembic]
+level = INFO
+handlers =
+qualname = alembic
+
+[handler_console]
+class = StreamHandler
+args = (sys.stderr,)
+level = NOTSET
+formatter = generic
+
+[formatter_generic]
+format = %(levelname)-5.5s [%(name)s] %(message)s
+datefmt = %H:%M:%S

alembic/README

@@ -0,0 +1,11 @@
+Generic single-database configuration with SQLite.
+
+To run the migrations:
+```
+alembic upgrade head
+```
+
+To generate a new migration (after modifying models):
+```
+alembic revision --autogenerate -m "description of changes"
+```

alembic/env.py

@@ -0,0 +1,83 @@
+from logging.config import fileConfig
+
+from sqlalchemy import engine_from_config
+from sqlalchemy import pool
+
+from alembic import context
+from app.models.base_model import Base
+# Import all models that should be included in migrations
+from app.models.product import Product  # noqa
+from app.models.cart import Cart, CartItem  # noqa
+
+# This is the Alembic Config object, which provides
+# access to the values within the .ini file in use.
+config = context.config
+
+# Interpret the config file for Python logging.
+# This line sets up loggers basically.
+if config.config_file_name is not None:
+    fileConfig(config.config_file_name)
+
+# Add your model's MetaData object here
+# for 'autogenerate' support
+target_metadata = Base.metadata
+
+# other values from the config, defined by the needs of env.py,
+# can be acquired:
+# my_important_option = config.get_main_option("my_important_option")
+# ... etc.
+
+
+def run_migrations_offline() -> None:
+    """Run migrations in 'offline' mode.
+
+    This configures the context with just a URL
+    and not an Engine, though an Engine is acceptable
+    here as well.  By skipping the Engine creation
+    we don't even need a DBAPI to be available.
+
+    Calls to context.execute() here emit the given string to the
+    script output.
+
+    """
+    url = config.get_main_option("sqlalchemy.url")
+    context.configure(
+        url=url,
+        target_metadata=target_metadata,
+        literal_binds=True,
+        dialect_opts={"paramstyle": "named"},
+    )
+
+    with context.begin_transaction():
+        context.run_migrations()
+
+
+def run_migrations_online() -> None:
+    """Run migrations in 'online' mode.
+
+    In this scenario we need to create an Engine
+    and associate a connection with the context.
+
+    """
+    connectable = engine_from_config(
+        config.get_section(config.config_ini_section, {}),
+        prefix="sqlalchemy.",
+        poolclass=pool.NullPool,
+    )
+
+    with connectable.connect() as connection:
+        is_sqlite = connection.dialect.name == "sqlite"
+        context.configure(
+            connection=connection,
+            target_metadata=target_metadata,
+            render_as_batch=is_sqlite,  # Key configuration for SQLite
+        )
+
+        with context.begin_transaction():
+            context.run_migrations()
+
+
+if context.is_offline_mode():
+    run_migrations_offline()
+else:
+    run_migrations_online()

alembic/script.py.mako

@@ -0,0 +1,24 @@
+"""${message}
+
+Revision ID: ${up_revision}
+Revises: ${down_revision | comma,n}
+Create Date: ${create_date}
+
+"""
+from alembic import op
+import sqlalchemy as sa
+${imports if imports else ""}
+
+# revision identifiers, used by Alembic.
+revision = ${repr(up_revision)}
+down_revision = ${repr(down_revision)}
+branch_labels = ${repr(branch_labels)}
+depends_on = ${repr(depends_on)}
+
+
+def upgrade() -> None:
+    ${upgrades if upgrades else "pass"}
+
+
+def downgrade() -> None:
+    ${downgrades if downgrades else "pass"}

alembic/versions/initial_migration.py

@@ -0,0 +1,78 @@
+"""initial migration
+
+Revision ID: 00001
+Revises: 
+Create Date: 2023-11-15
+
+"""
+from alembic import op
+import sqlalchemy as sa
+
+
+# revision identifiers, used by Alembic.
+revision = '00001'
+down_revision = None
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    # Create products table
+    op.create_table(
+        'products',
+        sa.Column('id', sa.Integer(), nullable=False),
+        sa.Column('created_at', sa.DateTime(timezone=True), server_default=sa.text('(CURRENT_TIMESTAMP)'), nullable=True),
+        sa.Column('updated_at', sa.DateTime(timezone=True), server_default=sa.text('(CURRENT_TIMESTAMP)'), nullable=True),
+        sa.Column('name', sa.String(length=255), nullable=False),
+        sa.Column('description', sa.Text(), nullable=True),
+        sa.Column('price', sa.Float(), nullable=False),
+        sa.Column('stock', sa.Integer(), nullable=False),
+        sa.Column('image_url', sa.String(length=512), nullable=True),
+        sa.Column('is_active', sa.Boolean(), nullable=False),
+        sa.PrimaryKeyConstraint('id')
+    )
+    op.create_index(op.f('ix_products_id'), 'products', ['id'], unique=False)
+    op.create_index(op.f('ix_products_name'), 'products', ['name'], unique=False)
+    
+    # Create carts table
+    op.create_table(
+        'carts',
+        sa.Column('id', sa.Integer(), nullable=False),
+        sa.Column('created_at', sa.DateTime(timezone=True), server_default=sa.text('(CURRENT_TIMESTAMP)'), nullable=True),
+        sa.Column('updated_at', sa.DateTime(timezone=True), server_default=sa.text('(CURRENT_TIMESTAMP)'), nullable=True),
+        sa.Column('user_id', sa.String(length=255), nullable=False),
+        sa.Column('is_active', sa.Integer(), nullable=False),
+        sa.PrimaryKeyConstraint('id')
+    )
+    op.create_index(op.f('ix_carts_id'), 'carts', ['id'], unique=False)
+    op.create_index(op.f('ix_carts_user_id'), 'carts', ['user_id'], unique=False)
+    
+    # Create cart_items table
+    op.create_table(
+        'cart_items',
+        sa.Column('id', sa.Integer(), nullable=False),
+        sa.Column('created_at', sa.DateTime(timezone=True), server_default=sa.text('(CURRENT_TIMESTAMP)'), nullable=True),
+        sa.Column('updated_at', sa.DateTime(timezone=True), server_default=sa.text('(CURRENT_TIMESTAMP)'), nullable=True),
+        sa.Column('cart_id', sa.Integer(), nullable=False),
+        sa.Column('product_id', sa.Integer(), nullable=False),
+        sa.Column('quantity', sa.Integer(), nullable=False),
+        sa.Column('unit_price', sa.Float(), nullable=False),
+        sa.ForeignKeyConstraint(['cart_id'], ['carts.id'], ondelete='CASCADE'),
+        sa.ForeignKeyConstraint(['product_id'], ['products.id'], ondelete='CASCADE'),
+        sa.PrimaryKeyConstraint('id'),
+        sa.UniqueConstraint('cart_id', 'product_id', name='uix_cart_product')
+    )
+    op.create_index(op.f('ix_cart_items_id'), 'cart_items', ['id'], unique=False)
+
+
+def downgrade() -> None:
+    op.drop_index(op.f('ix_cart_items_id'), table_name='cart_items')
+    op.drop_table('cart_items')
+    
+    op.drop_index(op.f('ix_carts_user_id'), table_name='carts')
+    op.drop_index(op.f('ix_carts_id'), table_name='carts')
+    op.drop_table('carts')
+    
+    op.drop_index(op.f('ix_products_name'), table_name='products')
+    op.drop_index(op.f('ix_products_id'), table_name='products')
+    op.drop_table('products')

app/api/v1/cart.py

@@ -0,0 +1,109 @@
+from fastapi import APIRouter, Depends, HTTPException, Header, status
+from sqlalchemy.orm import Session
+
+from app.db.session import get_db
+from app.schemas.cart import CartItemCreate, CartItemUpdate, CartDetail, CartItemResponse
+from app.schemas.common import DataResponse, ResponseBase
+from app.services import cart_service
+
+router = APIRouter(prefix="/cart", tags=["cart"])
+
+
+@router.get("", response_model=DataResponse[CartDetail])
+def get_cart(
+    user_id: str = Header(..., description="User ID for cart identification"),
+    db: Session = Depends(get_db)
+):
+    """
+    Get the current user's cart with all items.
+    """
+    cart = cart_service.get_active_cart(db, user_id)
+    cart_detail = cart_service.get_cart_detail(db, cart.id)
+    
+    return {
+        "success": True,
+        "message": "Cart retrieved successfully",
+        "data": cart_detail
+    }
+
+
+@router.post("/items", response_model=DataResponse[CartItemResponse], status_code=status.HTTP_201_CREATED)
+def add_to_cart(
+    item_data: CartItemCreate,
+    user_id: str = Header(..., description="User ID for cart identification"),
+    db: Session = Depends(get_db)
+):
+    """
+    Add a product to the user's cart.
+    """
+    cart_item, is_new = cart_service.add_item_to_cart(db, user_id, item_data)
+    
+    status_message = "Item added to cart successfully" if is_new else "Item quantity updated successfully"
+    
+    return {
+        "success": True,
+        "message": status_message,
+        "data": cart_item
+    }
+
+
+@router.put("/items/{item_id}", response_model=DataResponse[CartItemResponse])
+def update_cart_item(
+    item_id: int,
+    item_data: CartItemUpdate,
+    user_id: str = Header(..., description="User ID for cart identification"),
+    db: Session = Depends(get_db)
+):
+    """
+    Update the quantity of an item in the user's cart.
+    """
+    cart_item = cart_service.update_cart_item(db, user_id, item_id, item_data)
+    if not cart_item:
+        raise HTTPException(
+            status_code=status.HTTP_404_NOT_FOUND,
+            detail=f"Cart item with ID {item_id} not found in user's cart"
+        )
+    
+    return {
+        "success": True,
+        "message": "Cart item updated successfully",
+        "data": cart_item
+    }
+
+
+@router.delete("/items/{item_id}", response_model=ResponseBase)
+def remove_cart_item(
+    item_id: int,
+    user_id: str = Header(..., description="User ID for cart identification"),
+    db: Session = Depends(get_db)
+):
+    """
+    Remove an item from the user's cart.
+    """
+    success = cart_service.remove_cart_item(db, user_id, item_id)
+    if not success:
+        raise HTTPException(
+            status_code=status.HTTP_404_NOT_FOUND,
+            detail=f"Cart item with ID {item_id} not found in user's cart"
+        )
+    
+    return {
+        "success": True,
+        "message": "Item removed from cart successfully"
+    }
+
+
+@router.delete("", response_model=ResponseBase)
+def clear_cart(
+    user_id: str = Header(..., description="User ID for cart identification"),
+    db: Session = Depends(get_db)
+):
+    """
+    Remove all items from the user's cart.
+    """
+    cart_service.clear_cart(db, user_id)
+    
+    return {
+        "success": True,
+        "message": "Cart cleared successfully"
+    }

app/api/v1/health.py

@@ -0,0 +1,25 @@
+from fastapi import APIRouter, Depends
+from sqlalchemy.orm import Session
+
+from app.db.session import get_db
+
+router = APIRouter(prefix="/health", tags=["health"])
+
+
+@router.get("")
+def health_check(db: Session = Depends(get_db)):
+    """
+    Health check endpoint to verify the API is running correctly.
+    """
+    # Check database connection
+    try:
+        # Execute a simple query to check the database connection
+        db.execute("SELECT 1")
+        db_status = "healthy"
+    except Exception:
+        db_status = "unhealthy"
+
+    return {
+        "status": "ok",
+        "database": db_status,
+    }

app/api/v1/products.py

@@ -0,0 +1,105 @@
+from typing import Optional
+from fastapi import APIRouter, Depends, HTTPException, Query, status
+from sqlalchemy.orm import Session
+
+from app.db.session import get_db
+from app.schemas.product import Product, ProductCreate, ProductUpdate
+from app.schemas.common import PaginatedResponse, DataResponse
+from app.services import product_service
+
+router = APIRouter(prefix="/products", tags=["products"])
+
+
+@router.get("", response_model=PaginatedResponse[Product])
+def get_products(
+    skip: int = Query(0, ge=0),
+    limit: int = Query(100, ge=1, le=100),
+    is_active: Optional[bool] = None,
+    db: Session = Depends(get_db)
+):
+    """
+    Get a list of products with pagination and optional filtering.
+    """
+    products = product_service.get_products(db, skip=skip, limit=limit, is_active=is_active)
+    total = product_service.get_product_count(db, is_active=is_active)
+    
+    return {
+        "success": True,
+        "message": "Products retrieved successfully",
+        "data": products,
+        "total": total,
+        "page": skip // limit + 1 if limit > 0 else 1,
+        "size": limit,
+        "pages": (total + limit - 1) // limit if limit > 0 else 1
+    }
+
+
+@router.get("/{product_id}", response_model=DataResponse[Product])
+def get_product(product_id: int, db: Session = Depends(get_db)):
+    """
+    Get a specific product by ID.
+    """
+    product = product_service.get_product_by_id(db, product_id)
+    if not product:
+        raise HTTPException(
+            status_code=status.HTTP_404_NOT_FOUND,
+            detail=f"Product with ID {product_id} not found"
+        )
+    
+    return {
+        "success": True,
+        "message": "Product retrieved successfully",
+        "data": product
+    }
+
+
+@router.post("", response_model=DataResponse[Product], status_code=status.HTTP_201_CREATED)
+def create_product(product_data: ProductCreate, db: Session = Depends(get_db)):
+    """
+    Create a new product.
+    """
+    product = product_service.create_product(db, product_data)
+    
+    return {
+        "success": True,
+        "message": "Product created successfully",
+        "data": product
+    }
+
+
+@router.put("/{product_id}", response_model=DataResponse[Product])
+def update_product(
+    product_id: int, 
+    product_data: ProductUpdate, 
+    db: Session = Depends(get_db)
+):
+    """
+    Update an existing product.
+    """
+    product = product_service.update_product(db, product_id, product_data)
+    if not product:
+        raise HTTPException(
+            status_code=status.HTTP_404_NOT_FOUND,
+            detail=f"Product with ID {product_id} not found"
+        )
+    
+    return {
+        "success": True,
+        "message": "Product updated successfully",
+        "data": product
+    }
+
+
+@router.delete("/{product_id}", status_code=status.HTTP_204_NO_CONTENT, response_model=None)
+def delete_product(product_id: int, db: Session = Depends(get_db)):
+    """
+    Delete a product.
+    """
+    success = product_service.delete_product(db, product_id)
+    if not success:
+        raise HTTPException(
+            status_code=status.HTTP_404_NOT_FOUND,
+            detail=f"Product with ID {product_id} not found"
+        )
+    
+    return None

app/core/config.py

@@ -0,0 +1,27 @@
+from typing import List, Union
+from pydantic import AnyHttpUrl, validator
+from pydantic_settings import BaseSettings
+
+
+class Settings(BaseSettings):
+    API_V1_STR: str = "/api/v1"
+    PROJECT_NAME: str = "Simple Cart System"
+    PROJECT_DESCRIPTION: str = "A simple cart system API built with FastAPI and SQLite"
+    PROJECT_VERSION: str = "0.1.0"
+    
+    # CORS
+    BACKEND_CORS_ORIGINS: List[Union[str, AnyHttpUrl]] = ["http://localhost", "http://localhost:8000"]
+
+    @validator("BACKEND_CORS_ORIGINS", pre=True)
+    def assemble_cors_origins(cls, v: Union[str, List[str]]) -> Union[List[str], str]:
+        if isinstance(v, str) and not v.startswith("["):
+            return [i.strip() for i in v.split(",")]
+        elif isinstance(v, (list, str)):
+            return v
+        raise ValueError(v)
+
+    class Config:
+        case_sensitive = True
+
+
+settings = Settings()

app/db/session.py

@@ -0,0 +1,24 @@
+from pathlib import Path
+from sqlalchemy import create_engine
+from sqlalchemy.orm import sessionmaker
+
+# Set up database directory
+DB_DIR = Path("/app") / "storage" / "db"
+DB_DIR.mkdir(parents=True, exist_ok=True)
+
+SQLALCHEMY_DATABASE_URL = f"sqlite:///{DB_DIR}/db.sqlite"
+
+engine = create_engine(
+    SQLALCHEMY_DATABASE_URL,
+    connect_args={"check_same_thread": False}
+)
+
+SessionLocal = sessionmaker(autocommit=False, autoflush=False, bind=engine)
+
+# Create a dependency
+def get_db():
+    db = SessionLocal()
+    try:
+        yield db
+    finally:
+        db.close()

app/models/__init__.py

@@ -0,0 +1,6 @@
+# Re-export models for easier imports elsewhere
+from app.models.base_model import Base as Base
+from app.models.product import Product as Product
+from app.models.cart import Cart as Cart, CartItem as CartItem
+
+__all__ = ["Base", "Product", "Cart", "CartItem"]

app/models/base_model.py

@@ -0,0 +1,17 @@
+from sqlalchemy import Column, Integer, DateTime
+from sqlalchemy.ext.declarative import declarative_base
+from sqlalchemy.sql import func
+
+Base = declarative_base()
+
+
+class BaseModel(Base):
+    """Base model for all models to inherit from."""
+
+    __abstract__ = True
+
+    id = Column(Integer, primary_key=True, index=True)
+    created_at = Column(DateTime(timezone=True), server_default=func.now())
+    updated_at = Column(
+        DateTime(timezone=True), server_default=func.now(), onupdate=func.now()
+    )

app/models/cart.py

@@ -0,0 +1,31 @@
+from sqlalchemy import Column, String, Float, Integer, ForeignKey, UniqueConstraint
+from sqlalchemy.orm import relationship
+from app.models.base_model import BaseModel
+
+
+class Cart(BaseModel):
+    """Model for shopping cart."""
+
+    __tablename__ = "carts"
+
+    user_id = Column(String(255), nullable=False, index=True)
+    is_active = Column(Integer, default=1, nullable=False)
+    
+    items = relationship("CartItem", back_populates="cart", cascade="all, delete-orphan")
+
+
+class CartItem(BaseModel):
+    """Model for items in shopping cart."""
+
+    __tablename__ = "cart_items"
+    __table_args__ = (
+        UniqueConstraint("cart_id", "product_id", name="uix_cart_product"),
+    )
+
+    cart_id = Column(Integer, ForeignKey("carts.id", ondelete="CASCADE"), nullable=False)
+    product_id = Column(Integer, ForeignKey("products.id", ondelete="CASCADE"), nullable=False)
+    quantity = Column(Integer, nullable=False, default=1)
+    unit_price = Column(Float, nullable=False)  # Stores the price at the time of adding to cart
+    
+    cart = relationship("Cart", back_populates="items")
+    product = relationship("Product")

app/models/product.py

@@ -0,0 +1,15 @@
+from sqlalchemy import Column, String, Float, Integer, Text, Boolean
+from app.models.base_model import BaseModel
+
+
+class Product(BaseModel):
+    """Model for product items."""
+
+    __tablename__ = "products"
+
+    name = Column(String(255), nullable=False, index=True)
+    description = Column(Text, nullable=True)
+    price = Column(Float, nullable=False)
+    stock = Column(Integer, nullable=False, default=0)
+    image_url = Column(String(512), nullable=True)
+    is_active = Column(Boolean, default=True, nullable=False)

app/schemas/__init__.py

@@ -0,0 +1,31 @@
+# Re-export schemas for easier imports elsewhere
+from app.schemas.common import (
+    ResponseBase as ResponseBase,
+    DataResponse as DataResponse,
+    PaginatedResponse as PaginatedResponse,
+    PaginationParams as PaginationParams
+)
+from app.schemas.product import (
+    Product as Product,
+    ProductCreate as ProductCreate,
+    ProductUpdate as ProductUpdate,
+    ProductInDB as ProductInDB
+)
+from app.schemas.cart import (
+    CartBase as CartBase,
+    CartCreate as CartCreate,
+    CartResponse as CartResponse,
+    CartDetail as CartDetail,
+    CartItemBase as CartItemBase,
+    CartItemCreate as CartItemCreate,
+    CartItemUpdate as CartItemUpdate,
+    CartItemResponse as CartItemResponse,
+    CartItemDetail as CartItemDetail
+)
+
+__all__ = [
+    "ResponseBase", "DataResponse", "PaginatedResponse", "PaginationParams",
+    "Product", "ProductCreate", "ProductUpdate", "ProductInDB",
+    "CartBase", "CartCreate", "CartResponse", "CartDetail",
+    "CartItemBase", "CartItemCreate", "CartItemUpdate", "CartItemResponse", "CartItemDetail"
+]

app/schemas/cart.py

@@ -0,0 +1,77 @@
+from typing import List
+from pydantic import BaseModel, Field, validator
+
+
+class CartItemBase(BaseModel):
+    """Base schema for cart item data."""
+    product_id: int = Field(..., title="Product ID")
+    quantity: int = Field(..., title="Quantity", ge=1)
+    
+    @validator('quantity')
+    def validate_quantity(cls, v):
+        if v < 1:
+            raise ValueError('Quantity must be at least 1')
+        return v
+
+
+class CartItemCreate(CartItemBase):
+    """Schema for adding an item to a cart."""
+    pass
+
+
+class CartItemUpdate(BaseModel):
+    """Schema for updating a cart item."""
+    quantity: int = Field(..., title="New quantity", ge=1)
+    
+    @validator('quantity')
+    def validate_quantity(cls, v):
+        if v < 1:
+            raise ValueError('Quantity must be at least 1')
+        return v
+
+
+class CartItemResponse(CartItemBase):
+    """Schema for cart item data in API responses."""
+    id: int
+    unit_price: float
+    
+    class Config:
+        orm_mode = True
+
+
+class CartItemDetail(CartItemResponse):
+    """Schema for detailed cart item data including product details."""
+    product_name: str
+    subtotal: float
+    
+    class Config:
+        orm_mode = True
+
+
+class CartBase(BaseModel):
+    """Base schema for cart data."""
+    user_id: str = Field(..., title="User ID")
+    is_active: int = Field(1, title="Cart status")
+
+
+class CartCreate(CartBase):
+    """Schema for creating a new cart."""
+    pass
+
+
+class CartResponse(CartBase):
+    """Schema for cart data in API responses."""
+    id: int
+    created_at: str
+    
+    class Config:
+        orm_mode = True
+
+
+class CartDetail(CartResponse):
+    """Schema for detailed cart data including items."""
+    items: List[CartItemDetail] = []
+    total: float
+    
+    class Config:
+        orm_mode = True

app/schemas/common.py

@@ -0,0 +1,31 @@
+from typing import Generic, TypeVar, List, Optional
+from pydantic import BaseModel
+
+
+T = TypeVar('T')
+
+
+class PaginationParams(BaseModel):
+    """Schema for pagination parameters."""
+    skip: int = 0
+    limit: int = 100
+
+
+class ResponseBase(BaseModel):
+    """Base schema for API responses."""
+    success: bool
+    message: str
+
+
+class DataResponse(ResponseBase, Generic[T]):
+    """Schema for API responses with data."""
+    data: Optional[T] = None
+
+
+class PaginatedResponse(ResponseBase, Generic[T]):
+    """Schema for paginated API responses."""
+    data: List[T]
+    total: int
+    page: int
+    size: int
+    pages: int

app/schemas/product.py

@@ -0,0 +1,56 @@
+from typing import Optional
+from pydantic import BaseModel, Field, validator
+
+
+class ProductBase(BaseModel):
+    """Base schema for product data."""
+    name: str = Field(..., title="Product name", min_length=1, max_length=255)
+    description: Optional[str] = Field(None, title="Product description")
+    price: float = Field(..., title="Product price", ge=0.01)
+    stock: int = Field(..., title="Available quantity", ge=0)
+    image_url: Optional[str] = Field(None, title="Product image URL")
+    is_active: bool = Field(True, title="Product availability status")
+    
+    @validator('price')
+    def validate_price(cls, v):
+        if v < 0:
+            raise ValueError('Price must be positive')
+        return round(v, 2)
+
+
+class ProductCreate(ProductBase):
+    """Schema for creating a new product."""
+    pass
+
+
+class ProductUpdate(BaseModel):
+    """Schema for updating an existing product."""
+    name: Optional[str] = Field(None, title="Product name", min_length=1, max_length=255)
+    description: Optional[str] = Field(None, title="Product description")
+    price: Optional[float] = Field(None, title="Product price", ge=0.01)
+    stock: Optional[int] = Field(None, title="Available quantity", ge=0)
+    image_url: Optional[str] = Field(None, title="Product image URL")
+    is_active: Optional[bool] = Field(None, title="Product availability status")
+    
+    @validator('price')
+    def validate_price(cls, v):
+        if v is not None and v < 0:
+            raise ValueError('Price must be positive')
+        if v is not None:
+            return round(v, 2)
+        return v
+
+
+class ProductInDB(ProductBase):
+    """Schema for product data retrieved from the database."""
+    id: int
+    created_at: str
+    updated_at: str
+
+    class Config:
+        orm_mode = True
+
+
+class Product(ProductInDB):
+    """Schema for product data returned in API responses."""
+    pass

app/services/__init__.py

@@ -0,0 +1,26 @@
+# Re-export service functions for easier imports elsewhere
+from app.services.product_service import (
+    get_products as get_products,
+    get_product_by_id as get_product_by_id,
+    create_product as create_product,
+    update_product as update_product,
+    delete_product as delete_product,
+    get_product_count as get_product_count
+)
+
+from app.services.cart_service import (
+    get_active_cart as get_active_cart,
+    get_cart_with_items as get_cart_with_items,
+    get_cart_detail as get_cart_detail,
+    add_item_to_cart as add_item_to_cart,
+    update_cart_item as update_cart_item,
+    remove_cart_item as remove_cart_item,
+    clear_cart as clear_cart
+)
+
+__all__ = [
+    "get_products", "get_product_by_id", "create_product", "update_product",
+    "delete_product", "get_product_count", "get_active_cart", "get_cart_with_items",
+    "get_cart_detail", "add_item_to_cart", "update_cart_item", "remove_cart_item",
+    "clear_cart"
+]

app/services/cart_service.py

@@ -0,0 +1,213 @@
+from typing import Optional, Dict, Any, Tuple
+from sqlalchemy.orm import Session, joinedload
+from fastapi import HTTPException, status
+
+from app.models.cart import Cart, CartItem
+from app.schemas.cart import CartItemCreate, CartItemUpdate
+from app.services import product_service
+
+
+def get_active_cart(db: Session, user_id: str) -> Optional[Cart]:
+    """
+    Get the active cart for a user, or create one if it doesn't exist.
+    """
+    cart = db.query(Cart).filter(
+        Cart.user_id == user_id,
+        Cart.is_active == 1
+    ).first()
+    
+    if not cart:
+        cart = Cart(user_id=user_id, is_active=1)
+        db.add(cart)
+        db.commit()
+        db.refresh(cart)
+    
+    return cart
+
+
+def get_cart_with_items(db: Session, cart_id: int) -> Optional[Cart]:
+    """
+    Get a cart by ID with all its items.
+    """
+    return db.query(Cart).options(
+        joinedload(Cart.items)
+    ).filter(Cart.id == cart_id).first()
+
+
+def get_cart_detail(db: Session, cart_id: int) -> Dict[str, Any]:
+    """
+    Get detailed cart information including items and total.
+    """
+    cart = get_cart_with_items(db, cart_id)
+    if not cart:
+        return None
+    
+    items_with_details = []
+    total = 0.0
+    
+    for item in cart.items:
+        product = product_service.get_product_by_id(db, item.product_id)
+        if product:
+            subtotal = item.quantity * item.unit_price
+            total += subtotal
+            items_with_details.append({
+                "id": item.id,
+                "product_id": item.product_id,
+                "product_name": product.name,
+                "quantity": item.quantity,
+                "unit_price": item.unit_price,
+                "subtotal": subtotal
+            })
+    
+    return {
+        "id": cart.id,
+        "user_id": cart.user_id,
+        "is_active": cart.is_active,
+        "created_at": cart.created_at,
+        "items": items_with_details,
+        "total": round(total, 2)
+    }
+
+
+def add_item_to_cart(
+    db: Session, 
+    user_id: str, 
+    item_data: CartItemCreate
+) -> Tuple[CartItem, bool]:
+    """
+    Add an item to a user's active cart. Returns the cart item and a boolean
+    indicating if it's a new item (True) or an updated existing item (False).
+    """
+    # Get or create active cart
+    cart = get_active_cart(db, user_id)
+    
+    # Check if product exists and is available
+    product = product_service.get_product_by_id(db, item_data.product_id)
+    if not product:
+        raise HTTPException(
+            status_code=status.HTTP_404_NOT_FOUND,
+            detail=f"Product with ID {item_data.product_id} not found"
+        )
+    
+    if not product.is_active:
+        raise HTTPException(
+            status_code=status.HTTP_400_BAD_REQUEST,
+            detail=f"Product with ID {item_data.product_id} is not available"
+        )
+    
+    if product.stock < item_data.quantity:
+        raise HTTPException(
+            status_code=status.HTTP_400_BAD_REQUEST,
+            detail=f"Not enough stock available. Requested: {item_data.quantity}, Available: {product.stock}"
+        )
+    
+    # Check if the item already exists in the cart
+    cart_item = db.query(CartItem).filter(
+        CartItem.cart_id == cart.id,
+        CartItem.product_id == item_data.product_id
+    ).first()
+    
+    is_new = False
+    
+    if cart_item:
+        # Update existing item
+        new_quantity = cart_item.quantity + item_data.quantity
+        if new_quantity > product.stock:
+            raise HTTPException(
+                status_code=status.HTTP_400_BAD_REQUEST,
+                detail=f"Not enough stock available. Requested total: {new_quantity}, Available: {product.stock}"
+            )
+        cart_item.quantity = new_quantity
+    else:
+        # Create new item
+        is_new = True
+        cart_item = CartItem(
+            cart_id=cart.id,
+            product_id=item_data.product_id,
+            quantity=item_data.quantity,
+            unit_price=product.price
+        )
+        db.add(cart_item)
+    
+    db.commit()
+    db.refresh(cart_item)
+    return cart_item, is_new
+
+
+def update_cart_item(
+    db: Session, 
+    user_id: str, 
+    item_id: int, 
+    item_data: CartItemUpdate
+) -> Optional[CartItem]:
+    """
+    Update the quantity of an item in a user's active cart.
+    """
+    # Get active cart
+    cart = get_active_cart(db, user_id)
+    
+    # Find the cart item
+    cart_item = db.query(CartItem).filter(
+        CartItem.id == item_id,
+        CartItem.cart_id == cart.id
+    ).first()
+    
+    if not cart_item:
+        return None
+    
+    # Check product stock
+    product = product_service.get_product_by_id(db, cart_item.product_id)
+    if not product:
+        raise HTTPException(
+            status_code=status.HTTP_404_NOT_FOUND,
+            detail=f"Product with ID {cart_item.product_id} not found"
+        )
+    
+    if product.stock < item_data.quantity:
+        raise HTTPException(
+            status_code=status.HTTP_400_BAD_REQUEST,
+            detail=f"Not enough stock available. Requested: {item_data.quantity}, Available: {product.stock}"
+        )
+    
+    # Update quantity
+    cart_item.quantity = item_data.quantity
+    
+    db.commit()
+    db.refresh(cart_item)
+    return cart_item
+
+
+def remove_cart_item(db: Session, user_id: str, item_id: int) -> bool:
+    """
+    Remove an item from a user's active cart.
+    """
+    # Get active cart
+    cart = get_active_cart(db, user_id)
+    
+    # Find the cart item
+    cart_item = db.query(CartItem).filter(
+        CartItem.id == item_id,
+        CartItem.cart_id == cart.id
+    ).first()
+    
+    if not cart_item:
+        return False
+    
+    # Remove item
+    db.delete(cart_item)
+    db.commit()
+    return True
+
+
+def clear_cart(db: Session, user_id: str) -> bool:
+    """
+    Remove all items from a user's active cart.
+    """
+    # Get active cart
+    cart = get_active_cart(db, user_id)
+    
+    # Delete all cart items
+    deleted = db.query(CartItem).filter(CartItem.cart_id == cart.id).delete()
+    db.commit()
+    
+    return deleted > 0

app/services/product_service.py

@@ -0,0 +1,87 @@
+from typing import List, Optional
+from sqlalchemy.orm import Session
+
+from app.models.product import Product
+from app.schemas.product import ProductCreate, ProductUpdate
+
+
+def get_products(
+    db: Session, 
+    skip: int = 0, 
+    limit: int = 100, 
+    is_active: Optional[bool] = None
+) -> List[Product]:
+    """
+    Get a list of products with pagination and optional filtering.
+    """
+    query = db.query(Product)
+    
+    if is_active is not None:
+        query = query.filter(Product.is_active == is_active)
+    
+    return query.offset(skip).limit(limit).all()
+
+
+def get_product_by_id(db: Session, product_id: int) -> Optional[Product]:
+    """
+    Get a product by its ID.
+    """
+    return db.query(Product).filter(Product.id == product_id).first()
+
+
+def create_product(db: Session, product_data: ProductCreate) -> Product:
+    """
+    Create a new product.
+    """
+    db_product = Product(**product_data.dict())
+    db.add(db_product)
+    db.commit()
+    db.refresh(db_product)
+    return db_product
+
+
+def update_product(
+    db: Session, 
+    product_id: int, 
+    product_data: ProductUpdate
+) -> Optional[Product]:
+    """
+    Update an existing product.
+    """
+    db_product = get_product_by_id(db, product_id)
+    if not db_product:
+        return None
+    
+    # Update only provided fields
+    update_data = product_data.dict(exclude_unset=True)
+    for key, value in update_data.items():
+        setattr(db_product, key, value)
+    
+    db.commit()
+    db.refresh(db_product)
+    return db_product
+
+
+def delete_product(db: Session, product_id: int) -> bool:
+    """
+    Delete a product by its ID.
+    """
+    db_product = get_product_by_id(db, product_id)
+    if not db_product:
+        return False
+    
+    db.delete(db_product)
+    db.commit()
+    return True
+
+
+def get_product_count(db: Session, is_active: Optional[bool] = None) -> int:
+    """
+    Get the total count of products with optional filtering.
+    """
+    query = db.query(Product)
+    
+    if is_active is not None:
+        query = query.filter(Product.is_active == is_active)
+    
+    return query.count()

main.py

@@ -0,0 +1,46 @@
+from fastapi import FastAPI
+from fastapi.middleware.cors import CORSMiddleware
+
+from app.api.v1 import health, products, cart
+from app.core.config import settings
+from app.db.session import engine
+from app.models import base_model
+
+# Create tables if they don't exist
+base_model.Base.metadata.create_all(bind=engine)
+
+app = FastAPI(
+    title=settings.PROJECT_NAME,
+    description=settings.PROJECT_DESCRIPTION,
+    version=settings.PROJECT_VERSION,
+    openapi_url=f"{settings.API_V1_STR}/openapi.json",
+    docs_url="/docs",
+    redoc_url="/redoc",
+)
+
+# Set up CORS
+if settings.BACKEND_CORS_ORIGINS:
+    app.add_middleware(
+        CORSMiddleware,
+        allow_origins=[str(origin) for origin in settings.BACKEND_CORS_ORIGINS],
+        allow_credentials=True,
+        allow_methods=["*"],
+        allow_headers=["*"],
+    )
+
+# Include routers
+app.include_router(health.router, prefix=settings.API_V1_STR)
+app.include_router(products.router, prefix=settings.API_V1_STR)
+app.include_router(cart.router, prefix=settings.API_V1_STR)
+
+
+@app.get("/")
+async def root():
+    return {
+        "message": "Welcome to Simple Cart System API",
+        "documentation": "/docs",
+    }
+
+if __name__ == "__main__":
+    import uvicorn
+    uvicorn.run(app, host="0.0.0.0", port=8000)

requirements.txt

@@ -0,0 +1,8 @@
+fastapi>=0.104.1
+uvicorn>=0.24.0
+sqlalchemy>=2.0.23
+alembic>=1.12.1
+pydantic>=2.4.2
+pydantic-settings>=2.0.3
+python-multipart>=0.0.6
+ruff>=0.1.5